This invention relates to turbine engines, and to a method of preventing the turbine of a turbine engine from choking at high speed. More particularly, it relates to novel improvements to prevent air from compressor discharge to bypass the combustion system. The present invention concerns gas turbine engines for auxiliary power units on aircraft, spacecraft, missiles, and other vehicles.
A typical turbine scroll system is shown in FIG. 1. The prior art gas turbine engine 210 may contain a combustor scroll 240 with a spiral contour and gradual area reduction with one end open for gas inlet and a B-width 250 that covers the entire circumference for gas to exit. Thin sheet metal with a high temperature capability may be used to fabricate the body through a forming process and machined rings may be welded to the sheet metal to form specified interface characteristics and for structural reinforcement. The combustor scroll 240 may be supported at one end, suspended by axial fasteners 220, suspended by a suspension pin 230, or clamped (not shown). This prior art gas turbine engine 210 is adequate only for low cycle and low performance engines. For more advanced systems used on high performance vehicles, such as aircraft, the combustor scroll 240 must meet additional requirements.
Current needs for turbine scroll systems include the ability to control small amounts of gas leakage between components at various operating conditions for performance optimization. Two main operating conditions are an open-loop condition (e.g., ground maintenance or in-flight emergency power) in which the engine runs on its own power and a closed-loop condition (e.g., taxi condition and general flight conditions) in which the engine runs on the bleed gas of the main engine.
Being able to control the size of the B-width (gap between the combustor scroll 240 and associated structures to minimize the gas leakage that can adversely effect the engine performance) may be a concern during engine design and development. Controlling the size of the B-width becomes more critical when an engine is operated in dual modes. Keeping the size of the B-width constant and maintaining effective sealing for system performance and integrity is critical during all operating conditions and surges. A constant B-width size minimizes gas leakage and erosion between components that may cause excessive wear or fretting. Prior art systems usually require tight tolerances for the inner diameters and outer diameters of mating components and shields around surfaces to minimize leakage.
None of the prior art is specifically intended for high performance, high cycle applications, and some suffer from one or more of the following disadvantages:
a) excessive wear and fretting.
b) inability to maintain constant B-width size.
c) ineffective sealing.
d) gas leakage between components.
As can be seen, there is a need for an improved apparatus and method for an improved gas turbine engine system, which minimizes wear and fretting, maintains constant B-width size, and effectively seals to prevent gas leakage between components.